1. Field of the Invention
The present invention relates to a method of and an apparatus for simultaneously displaying a plurality of video images on a display screen based on video signals stored in a plurality of video memories.
2. Description of the Related Art
FIGS. 34(A) through 34(C) show operation of a conventional video display apparatus of a personal computer system. Some recent personal computers can be operated by a plurality of operating systems (OS). FIG. 34(A) shows a display screen operated by a first OS, or MS-WINDOWS (trademark of Microsoft Corp.), where an image generated by a second OS, or MS-DOS (trademark of Microsoft Corp.) is displayed in a window of the first OS. FIGS. 34(B) and 34(C) show address spaces of these two operating systems.
In order to display an image generated by the second OS within a window of the first OS in the conventional system, video data should be transferred from a video memory (VRAM) of the second OS to another video memory (A-VRAM) of the first OS as indicated by the arrow in FIGS. 34(B) and 34(C). Since the transfer of the video data is executed by a CPU, it requires quite a long time and causes undesirable delay to the other processing by the CPU. Such problems often arise when a plurality of video memories are used in the video display apparatus.